The present invention concerns an ultrasonic probe as set forth in the classifying portion of claim 1.
There are numerous possible uses for apparatuses of that kind in medical diagnostics, in particular in ultrasonic sonography. Thus, ultrasonic probes are used in particular in connection with medical ultrasonic apparatuses which are based on the Doppler principle and which generate ultrasonic signals which are suitable for a respective diagnostic purpose in the range of between about 1 and about 20 MHz. The ultrasonic probes are also adapted to (individual) frequencies of that kind in a corresponding manner.
Ultrasonic probes which are known from the state of the art usually consist of a piezoelectric crystal which is suitably electrically stimulated in order then to produce an ultrasonic signal, for example 2, 4, 8 or 16 MHz, the crystal having geometrical and electrical parameters which are intended for a respective frequency.
If there is then the intention in the context of diagnostic purposes to change the frequency, for example from 2 to 4 MHz or from 2 to 2.5 MHz, then the ultrasonic probe used is usually replaced by a probe which is appropriate suited to the new frequency band.
Particularly in the technical area of embolism detection by means of ultrasound, a new and medically significant area of use of transcranial Doppler sonography, there is the technical challenge of reliably and distinguishably detecting the occurrence of embolisms in a blood vessel which is monitored by means of ultrasound, an embolism in that respect being distinguished by reflection properties of the incident ultrasonic signal, that are characteristic in relation to the surrounding blood. It will of course be noted that it is still difficult to draw a distinction between true embolisms and (undesired) interference effects, for example artefacts which occur due to probe movement.
It has been found that in particular embolisms can be recognised and distinguished in addition by characteristic, frequency-dependent reflection properties of one or more incident ultrasonic signals, in which case for example the reflected signal at a first ultrasonic frequency can be markedly higher or lower than the corresponding reflected signal level at a second frequency.
For uses of that kind or other diagnostic ultrasonic uses in which an important aspect is substantially simultaneous introduction of a plurality of ultrasonic frequencies into an observation medium or an observation object, there are hitherto practically no suitable probe arrangements. On the contrary, the procedure adopted usually involves managing with a plurality of individual probes which are secured to a common carrier or supporting arrangement. Apart from mechanical difficulties or difficulties involved in coupling procedures however there is here in particular the problem of focusing the respective signals from the individual probes on a common observation point, for example at a location in a blood vessel, while problems in terms of adjustment and accuracy are obvious.
Therefore the object of the present invention is to provide an ultrasonic probe of the general kind set forth, which is suitable for simple and user-friendly multifrequency operation, that is to say which can simultaneously irradiate more than one ultrasonic frequency (or a coherent ultrasonic band) on to a focus point in the observation medium and receive the signal reflected therefrom.
That object is attained by the ultrasonic probe as set forth in claims 1, 2, 3 and 7 respectively.
Advantageously in that respectxe2x80x94due to the structural and geometrical unit of the single crystals involved or, in the case of the structure set forth in claim 1, only the one crystalxe2x80x94optimum, coincident focusing of the simultaneously irradiated, narrow-band carrier signals is always achieved, and in particular adjustment operations or setting operations by an operator are no longer required.
In addition it is possible in the manner according to the invention to produce an extremely compact probe which, both in terms of production and also in terms of practical use, exhibits marked advantages in regard to portability and operation.
In otherwise known manner the received reflected Doppler signal is then passedxe2x80x94preferably in multi-channel modexe2x80x94to an evaluation operation which can then be adapted in particular also for frequency- (pattern-) dependent embolism detection.
In that respect basically the ultrasonic probe according to the invention is suitable for any media to be monitored, without in any way being limited to blood vessels.
An essential feature of the invention also provides that the multifrequency signal for the ultrasonic sensor is a simultaneous and synchronised multifrequency signal, wherein the individual carrier frequencies are preferably in a non-harmonic relationship with each other.
Advantageous developments of the invention are described in the appendant claims.
It is thus particularly preferable for the single crystals which are disposed in mutually adjacent relationship in the coupling means to be so provided in a common introduction plane as to afford the desirable square shape each comprising two pairs of single crystals.
Both series and also parallel resonance apply as the resonance frequency in accordance with the invention, both for this embodiment and also for the further configurations of the invention.